U.s. Navy ship is joining the hunt for flight 370 over the Indian motion. The Australian prime minister saying the search zone is condensed, the underwater signals are now fating and fast. ABC's Clayton Sandell has more, now, from Perth, Australia. Clayton, good morning. Reporter: Good morning to you, Dan. This morning, officials tell us they are no longer hearing any credible signals from what they believe are emergency black box beacons. If that doesn't change, they will soon the have to give up part of the search. 14 ships and 10 airplanes spent another day in a frustrating search for clues. They are desperate to hear more of the underwater pings from beacons that would lead them to the airplane's cockpit voice and data recorders. But the fading signals have not been heard since Tuesday. Are you optimistic we will find these black boxes? We will do our best. Reporter: Now, the U.S. Navy captain in charge of this underwater probe, without new leads, they are forced to use plan "B." When the time is right, we'll say it's time to ship to the short range. Reporter: And that may be a few days away. Yes. Reporter: The next step in the search is using powerful sonar on this underwater drone to create images of the sea floor, as much as 15,000 feet down. Hoping the wreckage will appear among a pitch black alien landscape of plains, canyons and mountains. We got encouraging detections. But we're not going to be convinced we have found the aircraft until we can look at a picture and say, that is Malaysia air 370. Reporter: When or if the plane's black boxes are located, a vehicle like this will bring them up. The R.V. Will go down. And it will comb through the debris field, looking for the black boxes and any other items that investigators need to help identify the cause of the crash. Reporter: This morning, more resources are heading this way. The Navy is sending a resupply ship with more gas and more food. It's a sign of how long they The search could go on for months, even years.

This transcript has been automatically generated and may not be 100% accurate.

The Long and Complicated Task of Finding Flight 370

Missing Malaysia Flight 370 may be more difficult to locate without pings in water that may be 15,000 feet deep.

Missing Malaysian Plane: Signals Detected

Officials have the most "promising lead yet" in the search for Malaysian Airlines Flight 370.